Overall, there were an estimated 254.4 million registered passenger vehicles in the United States according to a 2007 DOT study

This number, along with the average age of vehicles, has increased steadily since 1960, indicating a growing number of vehicles per capita.

According to the US Bureau of Transit Statistics for 2006 there are 250,844,644 registered passenger vehicles in the US. Out of these roughly 251 million vehicles, 135,399,945 were classified as automobiles, while 99,124,775 were classified as "Other 2 axle, 4 tire vehicles," presumably SUVs and pick-up trucks.

Yet another 6,649,337 were classified as vehicles with 2 axles and 6 tires and 2,169,670 were classified as "Truck, combination." There were approximately 6,686,147 motorcycles in the US in 2006.

At least 920 million plus tires in use annually

Estimates of the U.S. vehicle fleet multiplied by 4 gives a very rough number for annual tires in use of more than 920 million tires. (1 billion tires in use if 250 million time 4--these numbers are conservative)

The Industry news coverage in Rubberworld: The Technical Service and News Website for the Rubber Industry

reports: “Total 2010 tire shipments are projected to increase to 282 million units from last year’s 260 million.” (2014 estimate of 233 million tires reach the scrap market)

Each year, about 300 million scrap tires are generated in the U.S. Of those, about 52 percent are used as TDF (tire derived fuel) in the cement industry, pulp and paper mills and by some utility and industrial boilers. Also reporting: “After decades of EPA-sanctioned use as a supplemental industrial fuel, EPA is proposing now to declare whole scrap tires a solid waste..”

“Approximately 280 million tires are discarded each year by American motorists, approximately one tire for every person in the United States. Around 30 million of these tires are retreaded or reused, leaving roughly 250 million scrap tires to be managed annually. About 85 percent of these scrap tires are automobile tires, the remainder being truck tires. Besides the need to manage these scrap tires, it has been estimated that there may be as many as 2 to 3 billion tires that have accumulated over the years and are contained in numerous stockpiles.(1)”

November 2014 Report , reports 303 million tires were discarded in 2007 including 257 million light duty passenger and light truck tires, weighing an average of 22.5 pounds and 45 million heavy truck tires weighing an average of 120 pounds. In 2013 the RMA estimated 233 million scrap tires were produced. Get the Report--

http://www.rma.org/scrap-tires/scrap-tires-the-environment/

The Rubber Manufacturer Association estimates that 1 tire is discarded per year for each U.S. citizen which would be 310 million tires discarded in 2010. “Table 2 illustrates that RMA has once again validated the estimate of one tire per person per year as the number of scrap tires generated annually in the U.S.” Page 5 Scrap tire generation rates, 9th Biennial Report.

The Rubber industry makes tonnage calculations of scrap tire amounts using an averaged weight for a tire of 37 pounds, this is an average of the heavier 120 truck tires (45 million tires) and light duty passenger vehicles weight of 22.5 pounds -( 257 million tires). My calculations below of 5 lbs per year of tread wear loss using 920 million tires underestimates the heavier wear on 45 million heavy truck tires per year. (RMA prior year Report not on web--see November 2014 Report)

Estimates from the turf industry which is analyzing the environmental effects of using tires in landscape applications, estimated about 5 pounds of weight is lost in tire wear from the average passenger car tire between a new weight of 25 lbs and a scrap weight of 20 lbs.

If the wear is distributed over two years instead of one the calculations below could be reduced by half Meaning it would take two years instead of one for the calculated amount of tire wear particle to be released into the U.S. air, land and water environment.

An Assessment of Environmental Toxicity and Potential Contamination from Artificial Turf using Shredded or Crumb Rubber

“It is estimated that over 80% of respirable particulate matter (PM10) in cities comes from road transport and that tire and brake wear are responsible for the 3–7% emission of it. Data on the indicators of environmental impact of tire debris (TD), originated from the tire abrasion on roads, are extremely scarce, even though TD contains chemicals (zinc and organic compounds) which can be released in the environment.”

“Tire wear particles (TWP) are released from the tire tread during use of the tires. The particles are formed as a result of the tread abrasion from the road surface. Tire wear itself is a complex physico-chemical process which is driven by the frictional energy developed at the interface between the tread and the road pavement. The amount of wear that occurs during a tire's lifetime varies enormously depending on its type and how it is used.”

“TWP consist of a complex mixture of rubber, asphalt, road dust, gravel, and other materials. TWP are released directly to the environment on both the road surface and suspended in the air. Subsequently the particles can be transported to the soil and surface water via road way run-off and air deposition.

A storm drain channel is colored grey from road dust drained from a busy highway in Louisville. Its I-64 over Beargrass Creek in Butchertown. (See Main Stem Album) Road dust is a mixture of pavement, chassis metal wear particles, combustion products and tire wear particulate or TWP.

X’s and O’s--Tires discarded make mosquito breeding grounds near I-64 below the Cliffs of Clifton. See it HERE

Mn, Zn and Cd were found to exist in the form of free ions and carbonate complexes. Stable organic complexes of Cu in road dust leachates

were strongly adsorbed by soakaway sediments despite the limited adsorption of Dissolved Organic Carbon. On the other hand, desorption of free Mn, Zn and Cd ions from the sediment receiving road dust leachates was observed, indicating that heavy metals such as Mn, Zn and Cd may ultimately reach groundwater as free ions.”

While sediments in infiltration facilities act as adsorbents that accumulate heavy metals, sediments with a high heavy metal content risk being swept into aquatic environments as well as shedding ions by desorption.”

Part of the toxic nature of rubber leachate is due to its mineral content: aluminum, cadmium, chromium, copper, iron, magnesium, manganese, molybdenum, selenium, sulfur, and zinc have all been identified Of

these minerals, rubber contains very high levels of zinc – as much as 2% of the tire mass.

The Myth of Rubberized Landscapes

“Automobile and truck tire-treads wear on roads and generate

tire-wear debris of various size ranges. Although most of the mass of tire-wear particles is from particles much larger than 10 μm, minor airborne and inhalable fractions are also generated.

Various studies have reported the direct and indirect adverse

health effects of the chemical components of tire-tread rubbers.

Tire treads are commonly composed of natural and/or

synthetic rubbers, carbon black, and extender oils, respectively,

accounting for 40-60%, ∼30%, and 10-20% by mass.

Small amounts (less than ∼2% each) of vulcanization accelerators, retarders, softeners, and antioxidants are also added during manufacture to obtain the desired properties. Carbon black and extender oils can be a source of high concentrations of polycyclic aromatic hydrocarbons (PAHs), including carcinogenic benzo[a]pyrene.”

“Another more subtle effect of tire wear on human health may be the presence of latex allergens. A recent epidemiological study revealed contemporaneous linear correlations between asthma mortality rates and radial-tire use, rather than with other traffic-related factors. More recently, evidence that organic extracts from tire rubber can cause localized damage to the plasma membrane of human lung epithelial cells has been reported. These findings stress the necessity of wide-scale monitoring to assess the relative importance of tire wear to urban air quality.”

Although the relative contribution of tire wear is not very high (e.g., 0.8% in rooftop SPM, Table 1), unambiguous detection of dihydroreisn acids clearly indicates the existence of tire-wear particles in ambient matrices at significant levels.

“The annual volume of dust resulting from tire wear, calculated based on the number of automobiles registered in Japan, was 1,747,245.4 m3.[cubic meters] To put it simply, this translates to approximately 1.4 times the volume of the Tokyo Dome, a famous Japanese baseball stadium.

--equivalent to the weight of 15.6 million barrels of oil at 294 lbs per barrel. The largest supertanker can carry 4.1 million barrels of oil, so a lot more than

4 ultra supertankers of tire rubber are spilled into our environment in the U.S every year using just 5 pounds of weight loss per tire annually.

920 million times 20 pounds of wear loss equals 18.4 billion pounds

equals 9.2 million tons of rubber tread loss annually If 20 pounds of annual wear is used -- 18.4 billion divided by 294 pounds per barrel is 62,585,034 barrels divided by 4.1 million barrels for the largest supertanker is 15.2 supertankers per year of tire wear in just the U.S. lost into the environment.

These numbers illustrate the heavy cost of individual automobile transportation when the fleet numbers are multiplied times oil, tire loss, rusting steel and metal wear. Substantial and profound transformation of the environment is every where visible and the effects on our health and environment are becoming more well understood.

“While the constituents of brake material may vary among manufacturers and over time, iron, copper, antimony, and barium have been associated with the particulate matter released from brake operation.”

The greater enhancement at the curbside site compared to the background sites of the concentrations of iron, copper, antimony, and barium than other elements (Table 1) confirms the findings of Gietl et al.,6 using data from 2007 obtained at this site, and by Birmili et al.26 in Birmingham, that these metals are associated with a traffic-related source. These metals have all been identified as constituents of vehicle brakes,4 although

usage will depend upon the manufacturer and specification of the brake, and other sources of these metals may be present.”

Brake dust and other road particulates discolors the shiny metal of a wheel in photo below

“Although numerous studies have been conducted on the toxicity of leachates from tire materials and road particles, there is no information available regarding the human and ecological toxicity potential of real world TWP.”

“Studies have shown that some of the chemicals that can leach out of tire components (such as zinc oxide, diphenylamines, 2-mercaptobenzothiazole, and PAHs) exhibit toxicity to aquatic organisms in laboratory tests; however, no studies have specifically evaluated the toxicity of the TWP under realistic environmental or biological conditions.”

“Additionally, corrosion of chassis, bodywork, and other vehicle components, as well as corrosion of road structures such as signs, crash barriers and fencing can contribute to nonexhaust particulate in traffic areas.”

“The abrasion and corrosion processes can also lead to the deposition of particles on the road surface. The material previously deposited on the road surface, often referred to as ‘road dust’, may also contain exhaust particles, de-icing salt and grit originating from winter maintenance, and matter from a range of sources that are not related to road transport (e.g. crustal and vegetative material, and material from industrial/commercial/domestic activity). The residual road dust can be suspended or resuspended in the atmosphere as a result of tire wear, vehiclegenerated turbulence, and wind dispersion. While non-exhaust emission sources may contribute significantly to atmospheric particle concentrations, the data relating to the emission rate, size, and composition of particles arising from such sources are not comprehensive.”

“It is estimated that over 80% of respirable particulate matter (PM10) in cities comes from road transport and that tire and brake wear are responsible for the 3–7% emission of it. Data on the indicators of environmental impact of tire debris (TD), originated from the tire abrasion on roads, are extremely scarce, even though TD contains chemicals (zinc and organic compounds) which can be released in the environment.”

Results

The solution of undiluted 50 g/L TD (tire dust) produced 80.2% mortality (p < 0.01) in X. laevis embryos and this toxic effect was three times greater than that produced by 100 g/L TD. Zn accumulation in HepG2 cells was evident after 4 h exposure. A549 cells exposed to TD organic extract for 72 h presented a modified morphology, a decrease in cell proliferation and an increase in DNA damage as shown by comet assay. The dose 80 μg/ml of TD extract produced 14.6% mortality in X. laevis embryos and 15.9% mortality at 120 μg/ml. Treatment with 80, 100, or 120 μg/ml TD organic extract increased from 14.8% to 37.8% malformed larvae percentages compared to 5.6% in the control.

Conclusion

Since the amount of Zn leached from TD(tire dust) is related to pH, aggregation of particles and elution process, the quantity of TD present in the environment has to be taken into account. Moreover the atmospheric conditions, which may deeply influence the particle properties, have to be considered. The TD organic fraction was toxic for cells and organisms. Thus, because of its chemical components, TD may have a potential environmental impact and has to be further investigated.

Previous work and these results confirm the significant role of zinc in leached TD (tire dust) and the presence of additional organic toxicants. The studies performed have focused their attention on the potential toxic risk to living aquatic organisms from whole rubber tires or scrap. In this study TD has been investigated for its impact on human cell lines and on X. laevis embryos. TD eluates contain zinc, and we have demonstrated that this metal can accumulate in cells, and affect X. laevis embryos. The TD organic extract was toxic to A549 cells and affected cell morphology, cell proliferation and DNA, and produced severe malformations in developing X. laevis embryos. These results contribute to the knowledge of a PM component, which represents a considerable PM10 percentage, which at present is not considered a 'hazardous substance", but it must be taken into account for its potential environmental impact [71,33]. Moreover, these results strongly stress the need for further investigation into the distribution of TD as well as on its fate in urban areas.

Tire debris (TD), generated from tire wear on roads, include particles with a size larger than 7 μm and range up to >100 μm, but also a population of smaller particles (<1 μm) [24], less than 20% of the total, according to Cadle and Williams [25]. More recently Fauser [26] examined the TD size distribution and concluded that it is a bimodal histogram with more than 90% by mass (in the range collected, i.e. <20 μm) smaller than 1 μm and the rest are larger than 7 μm. The total concentration of tire particles in a busy city road is in the range 1–10 μg/m3, with a mean value of 2.8 μg/m3 which represents about 5% of the total airborne particles <20 μm. From these data and those of Tappe and Null [27] and Ntziachristos [28] it can be calculated that the 5–7% of these particles are in the PM10 size range of the respirable fraction.

In a road simulator study, a significant source of sub-micrometer fine particles produced by the road–tire interface was observed. Since the particle size distribution and source strength is dependent on the type of tire used, it is likely that these particles largely originate from the tires, and not the road pavement. The particles consisted most likely of mineral oils from the softening filler and fragments of the carbon-reinforcing filler material (soot agglomerates). This identification was based on transmission electron microscopy studies of collected ultrafine wear particles and on-line thermal treatment using a thermodesorber.

The mean particle number diameters were between 15–50 nm, similar to those found in light duty vehicle (LDV) tail-pipe exhaust. A simple box model approach was used to estimate emission factors in the size interval 15–700 nm. The emission factors increased with increasing vehicle speed, and varied between 3.7×1011 and 3.2×1012 particles vehicle−1 km−1 at speeds of 50 and 70 km h−1. This corresponds to between 0.1–1% of tail-pipe emissions in real-world emission studies at similar speeds from a fleet of LDV with 95% gasoline and 5% diesel-fueled cars. The emission factors for particles originating from the road–tire interface were, however, similar in magnitude to particle number emission factors from liquefied petroleum gas-powered vehicles derived in test bench studies in Australia 2005. Thus the road–tire interface may be a significant contributor to particle emissions from ultraclean vehicles.

In the Deepwater Horizon oil well blow out, the government estimates some 4.9 million barrels of oil gushed into the Gulf, 800,000 of which was captured by surface ships. By comparison, every year, the abrasion of motor vehicle tires from some 280 million to 290 million U.S. vehicle tires, releases 4 times the Deepwater Horizon spill volume in TWP (tire wear particulate) composed of zinc, latex rubber, carbon black, polyaromatic hydrocarbons and other constituents. This volume is equivalent to 4 ultra supertanker capacities of tire rubber particulate spilled into the U.S. environment every year.

Studies show tire particulate chemicals are possibly carcinogenic, mutagenic, toxic to lung tissue, deadly to sensitive trout, fish and test species and plants. Researchers link air borne ultrafine tire wear particles - inhaled into the lungs - to a rise in asthma in urban areas.

“Williams et al. (1995) suggest that chronic exposure to respirable fragments of rubber that contain carbon black, latex antigens, and sulfur produce a number of health consequences. Respirable particles act as irritants, inducing nonspecific inflammation. Small particles suspended in polluted air have been significantly linked to hospital admissions for treatment of asthma, particularly in young children (Tseng et al. 1993 in Williams et al. 1995). Thus the rubber particles by themselves or in conjunction with other particulates could contribute to allergic responses in respiratory tissues by enhancing the allergic response caused by other airborne particles (Williams et al. 1995). Miguel et al. (1996) conclude that latex allergens or latex cross-reactive material present in sedimented and airborne particulate material, derived from tire debris, and generated by heavy urban vehicle traffic could be important factors in producing latex allergy and asthma symptoms associated with air pollution particles.”

This article seeks to answer--

How many cars are in the U.S. and how many tires in use annually ?

How many tires are worn out and replaced each year ?

Where does the disappearing tire wear go?

What are the human health effects and environmental effects of this tire wear and is it significant?

Good answers are developing for the first two questions, but the significant and important last question is a battleground of conflicting data in an emerging area of health and transportation science. Studies cited here vary from labeling tire dust particulate a significant human and environmental heath concern, to declaring levels in the environment of many tire wear particulates (TWPs) are not at significant levels.